The fundamental biological relevance of the transcription factor Yin Yang 1 (YY1) has been studied and described intensively in hundreds of publications. To date, however, only limited data of its structural and functional homologue YY2 are available. Especially, the impact of Yin Yang 2 (YY2) in the regulatory network of YY1 is almost unexplored. This article summarizes all critical aspects that are (or will be) relevant for a better understanding of YY1- and/or YY2-mediated cellular control mechanisms.